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November 29, 2011 11:55
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Building an event-sourced web application with Akka - Part 1
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case class InvoiceAddress(street: String, city: String, country: String) | |
case class InvoiceItem(description: String, count: Int, amount: BigDecimal) | |
case class Invoice( | |
id: String, | |
items: List[InvoiceItem] = Nil, | |
discount: Option[BigDecimal] = None, | |
sentTo: Option[InvoiceAddress] = None) extends EventSourced[InvoiceEvent, Invoice] { | |
def addItem(item: InvoiceItem): Update[InvoiceEvent, Invoice] = ... | |
def setDiscount(discount: BigDecimal): Update[InvoiceEvent, Invoice] = ... | |
def sendTo(address: InvoiceAddress): Update[InvoiceEvent, Invoice] = ... | |
def handle(event: InvoiceEvent): Invoice = event match { | |
case InvoiceItemAdded(_, item) => copy(items = item :: items) | |
case InvoiceDiscountSet(_, discount) => copy(discount = Some(discount)) | |
case InvoiceSent(_, to) => copy(sentTo = Some(to)) | |
} | |
} | |
sealed trait InvoiceEvent extends Event { def invoiceId: String } | |
case class InvoiceItemAdded(invoiceId: String, item: InvoiceItem) extends InvoiceEvent | |
case class InvoiceDiscountSet(invoiceId: String, discount: BigDecimal) extends InvoiceEvent | |
case class InvoiceSent(invoiceId: String, to: InvoiceAddress) extends InvoiceEvent | |
// ... |
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trait EventSourced[E <: Event, A <: EventSourced[E, A]] { | |
def update(event: E): Update[E, A] = Update.accept(event, handle(event)) | |
def handle(event: E): A | |
} | |
case class Invoice(...) extends EventSourced[InvoiceEvent, Invoice] { | |
// ... | |
def sendTo(address: InvoiceAddress): Update[InvoiceEvent, Invoice] = | |
if (items.isEmpty) Update.reject(DomainError("cannot send empty invoice")) | |
else update(InvoiceSent(id, address)) | |
def handle(event: Event): Invoice = event match { | |
// ... | |
case InvoiceSent(_, to) => copy(sentTo = Some(to)) | |
} | |
} |
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val invoice: Invoice = ... | |
invoice.sendTo(InvoiceAddress("foo", "bar", "baz")).result() match { | |
case Success(updated) => ... | |
case Failure(errors) => ... | |
} |
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invoice.sendTo(InvoiceAddress("foo", "bar", "baz")).result { (events: List[InvoiceEvent], updated: Invoice) => | |
// do something with generated events ... | |
// do something with updated invoice ... | |
} |
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val overallUpdate: Update[InvoiceEvent, Invoice] = for { | |
updated1 <- invoice.addItem(InvoiceItem("x", 1, 10)) | |
updated2 <- updated1.addItem(InvoiceItem("y", 2, 12)) | |
updated3 <- updated2.sendTo(InvoiceAddress("foo", "bar", "baz")) | |
} yield updated3 |
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val update = for { | |
created <- Invoice.create("test") | |
updated1 <- created.addItem(InvoiceItem("a", 1, 1)) | |
updated2 <- updated1.addItem(InvoiceItem("b", 2, 2)) | |
} yield updated2 | |
update.result { (events, updated) => | |
assert(updated == Invoice.handle(events.reverse)) // reconstruct Invoice from events | |
assert(events == List( | |
InvoiceItemAdded("test", InvoiceItem("b", 2, 2)), | |
InvoiceItemAdded("test", InvoiceItem("a", 1, 1)), | |
InvoiceCreated("test")) | |
) | |
} |
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